System for monitoring tension force of tendon in post-tensioning

ABSTRACT

A system for monitoring tension forces of tendons in post-tensioning includes a hydraulic jack to apply the tension force to the tendon, a hydraulic pump to supply a hydraulic pressure to the hydraulic jack, a digital elongation length measurement sensor to measure the elongation length of the piston, a measurement unit having a data logger adapted to receive and store the elongation length data measured by the digital elongation length measurement sensor and to send the elongation length data to a main server, a digital pressure measurement sensor, and a control module adapted to receive the elongation length data from the data logger or the main server, calculate the tension force, compensate for the coefficient of elasticity of the tendon according to the ratio of the real-time elongation length data to the pressure data, and compensate for the tension force calculated.

TECHNICAL FIELD

The present invention relates to a system for monitoring tension forcesof tendons in post-tensioning that accurately measures the tensionforces of the tendons and/or controls the tension forces introduced intothe tendons through a main server, thereby allowing the tension forcesto be applied uniformly to the tendons.

BACKGROUND ART

Post-tensioning is a method of applying prestress to concrete. In moredetail, tendons are tensioned and anchored in concrete after theconcrete has been cured to allow the tension forces to be introduced tothe tendons.

A plurality of tendons are arranged in concrete beams or slabs, and inthis case, it is important to minimize the deviation in the tensionforces introduced to the plurality of tendons so as to allow the tensionforces to be applied uniformly to the plurality of tendons. It isactually recommended that the error range between a designed tensionforce and a real tension force is controlled within the average of 7%and to the maximum of 13%.

In conventional post-tensioning, the tension force of the tendon ismeasured by reading the pressure gauge of a pressure pump and bymeasuring the moving distance of a piston of a hydraulic jack.

However, the conventional measuring methods are carried out in an analogway, thereby undesirably needing many labors in monitoring the tensionforces of the tendons.

Further, the pressure gauge or the moving distance of the piston ismeasured by a checker, and at the same time, the buttons for stoppingthe tensioning are pressed manually to control the tension forces of thetendons, so that the tension forces of the tendons are differentlyapplied every time. That is, there are many differences in themeasurement and control of the tension forces, constructability, andworking time according to the skill level of a worker, thereby making itdifficult to conduct accurate tensioning.

Moreover, the elongation length of the tendon after the tensioning ismeasured by a ruler to check the error range, but the elongation lengthsof the tendons may be different from each other according to thefriction coefficients of the tendons or the lengths of steel strands, sothat even if the elongation lengths are measured, there is no method ofaccurately recognizing the sizes of the tension forces applied to thetendons.

In addition, the pressure gauge data or the moving distance data of thepiston and the elongation length data measured by the ruler are providedonly by the record of the worker on the construction site, so that onlythe values on the record exist as database.

Accordingly, it is impossible to accurately measure the tension forcesof the tendons so that error control is meaningless.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made in view of theabove-mentioned problems occurring in the prior art, and it is an objectof the present invention to provide a system for monitoring tensionforces of tendons in post-tensioning that accurately measures thetension forces of the tendons and/or controls the tension forcesintroduced into the tendons through a main server, thereby allowing thetension forces to be applied uniformly to the tendons.

Technical Solution

To accomplish the above-mentioned object, according to the presentinvention, there is provided a system for monitoring tension forces oftendons disposed inside a concrete structure in post-tensioning, thesystem including: a hydraulic jack coupled to one tendon at one end ofthe concrete structure to apply the tension force to the tendon by theforward movement of a piston; a hydraulic pump connected to thehydraulic jack by a hydraulic pressure supply pipe to supply a hydraulicpressure to the hydraulic jack; a digital elongation length measurementsensor disposed on the hydraulic jack to measure the elongation lengthof the piston; a measurement unit having a data logger adapted toreceive and store the elongation length data measured by the digitalelongation length measurement sensor and to send the elongation lengthdata to a main server; a digital pressure measurement sensor disposed onthe hydraulic pressure supply pipe of the hydraulic pump; and a controlmodule adapted to receive the elongation length data from the datalogger or the main server, calculate the tension force, compensate forthe coefficient of elasticity of the tendon according to the ratio ofthe real-time elongation length data to the pressure data, andcompensate for the tension force calculated.

According to the present invention, desirably, if the pressure datameasured by the digital pressure measurement sensor reaches a set value,the hydraulic pump is controlled by the control module to stop theoperation of the hydraulic jack.

According to the present invention, desirably, the measurement unitincludes a near field communication module for transmitting thecollected data to a mobile terminal, and the mobile terminal transmitsthe received data to the main server.

According to the present invention, desirably, a reference point ismarked on one side of the tendon exposed to the outside of the concretestructure, and a position sensor is disposed on one side of thehydraulic jack to measure the moving distance of the reference point, sothat after the operation of the hydraulic jack stops by the controlmodule, the compensation for the elongation length is performedaccording to the moving distance of the reference point measured by theposition sensor.

Advantageous Effects

According to the present invention, the system for monitoring tensionforces of tendons in post-tensioning has the following advantages.

Firstly, the elongation length of the piston of the hydraulic jack canbe accurately measured through the digital elongation length measurementsensor and the measured elongation length is multiplied by thecoefficient of elasticity of the tendon to accurately measure thetension force of each tendon, so that the tension forces introduced tothe plurality of tendons can be controlled through the main server,thereby permitting the controlled tension forces to be uniformly appliedto the plurality of tendons.

Secondly, if the digital pressure measurement sensor is provided, thepressure of the fluid supplied to the hydraulic jack from the hydraulicpump can be measured to calculate the tension force of the tendon, sothat in addition to the measurement of the tension force of the tendonusing the elongation length of the piston of the hydraulic jack, thetension force of the tendon can be doubly measured through the digitalpressure measurement sensor, thereby making it possible to calculate thetension force of the tendon more accurately.

Thirdly, the hydraulic pump is controlled with the pressure data toallow the operation of the hydraulic jack to stop, thereby preventingthe tendon from being momentarily yielded.

Fourthly, the near field communication module is disposed in themeasurement unit so that the tension force of the tendon can bemonitored in real time through the mobile terminal in any place.

Lastly, the tension force of the tendon can be measured and controlledin real time through the digitalized system unlike the conventionalanalog type tension force measurement method, so that through anautomatic working process, material costs and labor costs can bedrastically reduced to provide many economical advantages.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side view showing a system for monitoring tension forces oftendons in post-tensioning according to the present invention.

FIG. 2 is a block diagram showing a measurement unit of the systemaccording to the present invention.

FIG. 3 is a side view showing the system for monitoring tension forcesof tendons in post-tensioning according to the present invention,wherein a digital pressure measurement sensor is further provided.

FIG. 4 is a side view showing the system for monitoring tension forcesof tendons in post-tensioning according to the present invention,wherein a mobile terminal is further provided.

FIG. 5 is a block diagram showing the system for monitoring tensionforces of tendons in post-tensioning according to the present invention.

FIG. 6 is a sectional view showing a hydraulic jack having a positionsensor.

BEST MODE FOR INVENTION

The present invention relates to a system for monitoring tension forcesof tendons disposed inside a concrete structure in post-tensioning, thesystem including: a hydraulic jack coupled to one tendon at one end ofthe concrete structure to apply the tension force to the tendon by theforward movement of a piston; a hydraulic pump connected to thehydraulic jack by a hydraulic pressure supply pipe to supply a hydraulicpressure to the hydraulic jack; a digital elongation length measurementsensor disposed on the hydraulic jack to measure the elongation lengthof the piston; a measurement unit having a data logger adapted toreceive and store the elongation length data measured by the digitalelongation length measurement sensor and to send the elongation lengthdata to a main server; a digital pressure measurement sensor disposed onthe hydraulic pressure supply pipe of the hydraulic pump; and a controlmodule adapted to receive the elongation length data from the datalogger or the main server, calculate the tension force, compensate forthe coefficient of elasticity of the tendon according to the ratio ofthe real-time elongation length data to the pressure data, andcompensate for the tension force calculated.

MODE FOR INVENTION

Hereinafter, an explanation on a system for monitoring tension forces oftendons in post-tensioning according to the present invention will be indetail given with reference to the attached drawing.

FIG. 1 is a side view showing a system for monitoring tension forces oftendons in post-tensioning according to the present invention, and FIG.2 is a block diagram showing a measurement unit of the system accordingto the present invention.

According to the present invention, a system for monitoring tensionforces of tendons in post-tensioning serves to control the tensionforces of tendons 11 disposed inside a concrete structure 1.

In post tensioning where after concrete is cured, the tendons 11 likesteel bars are tensioned and anchored in the concrete to introduce thetension thereto, that is, the system according to the present inventionmeasures the individual tension forces of the tendons 11 disposed inconcrete beams or slabs to allow the tension forces to be applieduniformly to the tendons 11.

As shown in FIG. 1, the system for monitoring the tension forces of thetendons in post-tensioning according to the present invention includes:a hydraulic jack 2 coupled to one tendon 11 at one end of the concretestructure 1 to apply the tension force to the tendon 11 by the forwardmovement of a piston 21; a hydraulic pump 3 connected to the hydraulicjack 2 by a hydraulic pressure supply pipe 31 to supply a hydraulicpressure to the hydraulic jack 2; a digital elongation lengthmeasurement sensor 4 disposed on the hydraulic jack 2 to measure theelongation length of the piston 21; a measurement unit 5 having a datalogger 51 adapted to receive and store the elongation length datameasured by the digital elongation length measurement sensor 4 and tosend the elongation length data to a main server 6; a digital pressuremeasurement sensor 8 disposed on the hydraulic pressure supply pipe 31of the hydraulic pump 3; and a control module 7 adapted to receive theelongation length data from the data logger 51 or the main server 6,calculate the tension force of the tendon 11, compensate for thecoefficient of elasticity of the tendon 11 according to the ratio of thereal-time elongation length data to the pressure data, and compensatefor the tension force calculated.

The tension force of the tendon 11 is proportional to the elongationlength of the tendon 11 like the steel bar. The elongation length of thetendon 11 is the same as the elongation length of the piston 21 of thehydraulic jack 2, and according to the present invention, therefore, theelongation length of the piston 21 of the hydraulic jack 2 is accuratelymeasured by the digital elongation length measurement sensor 4.

The digital elongation length measurement sensor 4 includes anextensometer.

The main server 6 stores and controls the measured data like theelongation length data, and through the main server 6, the tension forceof the tendon 11 can be monitored in real time even in an office room.

The main server 6 is connected to the data logger 51 of the measurementunit 5 through a network and stores the data collected by the datalogger 51 in a database 61, performs the classification, calculation,statisticalization and output of the data, and automatically calculatesa maximum value in an error rate or a mean value of the data.

The control module 7 multiplies a strain rate obtained from theelongation length of the piston 21 of the hydraulic jack 2 measured bythe digital elongation length measurement sensor 4 by the coefficient ofelasticity of the tendon 11 and the effective area of the tendon 11 tocalculate the tension force of the tendon 11.

The control module 7 is mounted on any one of the hydraulic pump 3, thedata logger 51, the main server 6, and a portable mobile terminal 9 aswill be discussed later, or it may be separately provided. Otherwise, asshown in FIG. 2, the control module 7 may be provided in the measurementunit 5.

As shown in FIG. 2, a switch box 53 of the measurement unit 5 receivesthe data from the digital elongation length measurement sensor 4, andthe data introduced to the switch box 53 is primarily processed throughthe data logger 51 and then sent to the main server 6 or the mobileterminal 9.

According to the present invention, as mentioned above, the elongationlength of the piston 21 of the hydraulic jack 2 is accurately measuredby the digital elongation length measurement sensor 4, and theelongation length of the piston 21 is multiplied by the coefficient ofelasticity of the tendon 11 to accurately measure the tension force ofthe tendon 11. Accordingly, the tension forces introduced to theplurality of tendons 11 can be converged and controlled by the mainserver 6.

FIG. 3 is a side view showing the system for monitoring tension forcesof tendons in post-tensioning according to the present invention,wherein a digital pressure measurement sensor is further provided, FIG.4 is a side view showing the system for monitoring tension forces oftendons in post-tensioning according to the present invention, wherein amobile terminal is further provided, and FIG. 5 is a block diagramshowing the system for monitoring tension forces of tendons inpost-tensioning according to the present invention.

As shown in FIG. 3, the digital pressure measurement sensor 8 isdisposed on the hydraulic pressure supply pipe 31 of the hydraulic pump3.

Since there is a given time difference between the hydraulic pressuresupply from the hydraulic pump 3 and the elongation of the piston 21 ofthe hydraulic jack 2, the elongation length of the piston 21 having thesame value as the elongation length of the tendon 11 is directlymeasured to calculate the tension force of the tendon 11, which is mostaccurate. If the tendon 11 slips from the hydraulic jack 2, however, itis more accurate to calculate the tension force of the tendon 11 throughthe pressure data measured by the digital pressure measurement sensor 8.

In addition to the calculation of the tension force of the tendon 10using the elongation length of the piston 21 of the hydraulic jack 2obtained by the digital elongation length measurement sensor 4, thehydraulic pressure of the fluid supplied from the hydraulic pump 3 tothe hydraulic jack 2 can be additionally measured by the digitalpressure measurement sensor 8 to calculate the tension force of thetendon 10.

If the tension force of the tendon 10 is measured doubly by the digitalelongation length measurement sensor 4 and the digital pressuremeasurement sensor 8, the tension force can be more accuratelycalculated.

At this time, if the pressure data measured by the digital pressuremeasurement sensor 8 reaches a set value, the hydraulic pump 3 iscontrolled by the control module 7 to stop the operation of thehydraulic jack 2.

In conventional practices wherein the hydraulic jack 2 is manipulatedmanually, the stop point of the piston 21 of the hydraulic jack 2 islost to cause the tendon 11 to be momentarily yielded.

Accordingly, as shown in FIG. 4, the control module 7 controls thehydraulic pump 3 using the pressure data to stop the operation of thehydraulic jack 2.

Of course, the hydraulic jack 2 may stop through the monitoring of theelongation length data, but as mentioned above, there is a given timedifference between the hydraulic pressure supply from the hydraulic pump3 and the elongation of the piston 21 of the hydraulic jack 2. If thehydraulic pump 3 is controlled through the elongation length data,accordingly, the stop point of the piston 21 of the hydraulic jack 2 maybe lost to cause the tendon 11 to be undesirably yielded, so that it isdesirable to control the hydraulic pump 3 through the pressure data.

Most desirably, the tension force of the tendon 11 is calculated throughthe elongation length data, and the operation of the hydraulic pump 3 iscontrolled through the pressure data.

If the digital pressure measurement sensor 8 is disposed on thehydraulic pressure supply pipe 31 of the hydraulic pump 3, the controlmodule 7 compensates for the tension force calculated according to theratio of the real-time elongation length data to the pressure data.

Since the tendon 11 like the steel bar has the elastic behavior beforeyielded, it is concluded that the tension force of the tendon 11 isproportional to the elongation length of the piston 21, but the tendon11 has a partially non-elastic behavior in the section except an elasticsection, so that it does not have the elastic behavior accurately andperfectly. So as to calculate an accurate constant, accordingly, thecontrol module 7 compensates for the coefficient of elasticity of thetendon 11 according to the ratio of the real-time elongation length datato the pressure data.

As shown in FIGS. 4 and 5, the measurement unit 5 includes a near fieldcommunication module 52 for transmitting the collected data to themobile terminal 9, and the mobile terminal 9 transmits the received datato the main server 6.

The mobile terminal 9 is a smartphone, and the near field communicationmodule 52 performs NFC (Near Field Communication), Bluetooth, ZigBee,infrared ray communication, UWB (Ultra-wideband) and the like.

FIG. 5 shows the case wherein the control module 7 is installed in anapplication of the mobile terminal 9, and so as to control the hydraulicpump 3 by the control module 7, in this case, the hydraulic pump 3 hasto have a communication module for receiving the signal from the mobileterminal 9.

The mobile terminal 9 like a user's smartphone is placed between themain server 6 and the data logger 51.

The data logger 51 transmits the data through the near fieldcommunication module 52, and accordingly, no internet environment isseparately needed.

The data collected in the measurement unit 5 can be checked directly bythe mobile terminal 9 of the user on the construction site.

If the mobile terminal 9 is the smartphone, moreover, a data measurementapplication is installed, and next, the control module 7 is installed inthe data measurement application.

At this time, the main server 6 transmits the collected data to amanager's terminal like PC, smartphone and so on through internet, sothat the data can be checked even at the long distance from theconstruction site. In case of the smartphone, the data can be checkedthrough a data view application.

The data view application and the data measurement application may bethe same as each other.

FIG. 6 is a sectional view showing the hydraulic jack having a positionsensor.

As shown in FIG. 6, a reference point 12 is marked on one side of thetendon 11 exposed to the outside of the concrete structure 1, and aposition sensor 10 is disposed on one side of the hydraulic jack 2 tomeasure the moving distance of the reference point 12, so that after theoperation of the hydraulic jack 2 stops by the control module 7, thecompensation for the elongation length is performed according to themoving distance of the reference point 12 measured by the positionsensor 10.

The value measured by the digital elongation length measurement sensor 4or the digital pressure measurement sensor 8 is obtained at the maximumforward moving length point of the piston 21 of the hydraulic jack 2.

If the hydraulic pressure of the hydraulic jack 2 is released, however,the tension force of the tendon 11 is partially released to cause thetendon 11 to be returned by a given length, so that a wedge is engagedwith the tendon 11 and fixed to the tendon 11.

Accordingly, there is a difference between the tension force at the timepoint when the hydraulic pressure of the hydraulic jack 2 is releasedand the tension force at the time point when the wedge is fixed to thetendon 11, so that the real tension force is somewhat smaller than themeasured tension force.

Accordingly, the elongation length is measured by the position sensor 10to compensate for the real tension force of the tendon 11, so that thetension force of the tendon 11 can be more accurately measured.

While the tension force is being applied to the tendon 11, in moredetail, the reference point 12 marked on one side of the tendon 11 ismoved backward from the concrete structure 1, and if the tension forceis released from the tendon 11, the reference point 12 is moved forwardin a reverse direction thereof until the tendon 11 is fixedly engagedwith the wedge after the fixation of the tendon 11 to the hydraulic jack2 has been released. At this time, the position sensor 10 measures theforward moving length of the tendon 11.

INDUSTRIAL APPLICABILITY

The present invention can accurately measure the elongation length ofthe piston of the hydraulic jack through the digital elongation lengthmeasurement sensor and multiply the measured elongation length by thecoefficient of elasticity of the tendon to accurately measure thetension force of each tendon, so that the tension forces introduced intothe plurality of tendons can be controlled through the main server,thereby permitting the controlled tension forces to be uniformly appliedto the plurality of tendons. Further, the pressure of the fluid suppliedto the hydraulic jack from the hydraulic pump can be measured throughthe digital pressure measurement sensor to measure the tension force ofthe tendon, so that in addition to the measurement of the tension forceof the tendon using the elongation length of the piston of the hydraulicjack, the tension force of the tendon can be doubly measured through thedigital pressure measurement sensor, thereby making it possible tocalculate the tension force of the tendon more accurately.

What is claimed is:
 1. A system for monitoring the tension forces oftendons disposed inside a concrete structure in post-tensioning, thesystem comprising: a hydraulic jack coupled to one tendon at one end ofthe concrete structure to apply the tension force to the tendon by theforward movement of a piston; a hydraulic pump connected to thehydraulic jack by a hydraulic pressure supply pipe to supply a hydraulicpressure to the hydraulic jack; a digital elongation length measurementsensor disposed on the hydraulic jack to measure the elongation lengthof the piston; a measurement unit having a data logger adapted toreceive and store the elongation length data measured by the digitalelongation length measurement sensor and to send the elongation lengthdata to a main server; a digital pressure measurement sensor disposed onthe hydraulic pressure supply pipe of the hydraulic pump; and a controlmodule adapted to receive the elongation length data from the datalogger or the main server, calculate the tension force, compensate forthe coefficient of elasticity of the tendon according to the ratio ofreal-time elongation length data to pressure data, and compensate forthe tension force calculated.
 2. The system according to claim 1,wherein if the pressure data measured by the digital pressuremeasurement sensor reaches a set value, the hydraulic pump is controlledby the control module to stop the operation of the hydraulic jack. 3.The system according to claim 1, wherein the measurement unit comprisesa near field communication module for transmitting the collected data toa mobile terminal, and the mobile terminal transmits the received datato the main server.
 4. The system according to claim 1, wherein areference point is marked on one side of the tendon exposed to theoutside of the concrete structure, and a position sensor is disposed onone side of the hydraulic jack to measure the moving distance of thereference point, so that after the operation of the hydraulic jack stopsby the control module, the compensation for the elongation length isperformed according to the moving distance of the reference pointmeasured by the position sensor.